Certain known security systems rely on the most sophisticated memory system available, i.e., the human brain, to secure digital data against unauthorized use or manipulation. Systems of this type accept account codes and also secret codes from an individual for encoding in accordance with a coding scheme that is controlled by such code words to yield a compiled code word of fixed word length despite the length of the applied code words (see, for example, U.S. Pat. No. 3,938,091, entitled "Personal Verification System", issued on Feb. 10, 1976). One difficulty encountered in a security system of this type is that a vast number of institutions relying in common upon such security systems require additional security against possible interactions of such encoded data between institutions, or between different stations within an institution.
Accordingly, in accordance with a preferred embodiment of the present invention, an additional control word is applied to the encoding logic to establish a unique encryption scheme for a given institution, or at a given secured location which is a function of the control word. Thus, a large number of the order of one billion distinctive encryption schemes may by provided for operation on a comparably large number of different combinations of code words that may possibly be applied thereto.